We are investigating the psychophysiological locus of aging and amphetamine effects using event related potentials (ERPs) and reaction times. Three different groups are currently under study: (a) females ages 30 - 50, (b) females ages 60 - 70, and (c) a special group of elderly in their late seventies and early eighties. These three groups are studied off stimulants using three tasks: 1) a task which independently varies stimulus and response complexity, 2) an auditory (Sternberg) memory task, and 3) a visual (Sternberg) memory task. Task differences are used to assess the relative differences in these groups. Reaction time measures and the latencies of two ERP components (N2 and P3) are used to determine if response selection or stimulus evaluation processes account for the observed deficits. Two of these groups (30 -50 and 60 - 70) are then studied under four different dosages of stimulant (placebo, 5, 10 and 20 milligrams methylphenidate) using the visual memory and stimulus-response paradigms. The aim of this work is to determine if amphetamine operates on a specific stage of information processing, and, if so, whether the processes enhanced by stimulants differ from those which appear to be the locus of the aging deficit.